Friction furnace



FIG. 1 is a top plan view of a friction furnace, showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a right side elevational view thereof;

FIG. 4 is a rear elevational view thereof; and

FIG. 5 is a left side elevational view thereof.

The ornamental design for a friction furnace, as shown and described.